Propeller

ABSTRACT

A propeller. The blades of the propeller are characterized by a blade center axis which corresponds to a generator line of a cone to which the blade, or blade thrust surface, conforms. The propeller hub is fixed to the blade at the root, in line with the blade center axis, such that the hub axis and blade center axis lie in the same plane, and the leading edge of the blade is positioned forward (referring to the upstream direction of movement caused by the propeller) of the trailing edge of the blade.

FIELD OF THE INVENTIONS

The inventions described below relate to the field of nautical and aeronautical propellers.

BACKGROUND OF THE INVENTIONS

Most propellers use blades which conform to the shape of a screw. These are referred to as helicoidal propellers. Helicoidal propellers create a large amount of turbulence compared to the thrust they generate, and various modifications are employed to decrease turbulence and increase thrust. Other forms of propellers have been proposed, but not widely adopted.

SUMMARY

The propellers described below provide for increased thrust and decreased turbulence with blades shaped to conform to the surface of a cone. Each blade is characterized by a blade center axis which corresponds to a generator line of a cone to which the blade, or blade thrust surface, conforms. The propeller hub is fixed to each blade at the root, in line with the blade center axis, such that the hub axis and blade center axis lie in the same plane, and the leading edge of the blade is positioned forward (referring to the upstream direction of movement caused by the propeller) of the trailing edge of the blade.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an aft perspective view of a marine propeller.

FIG. 2 illustrates the form of the propeller blades in relation to a hypothetical cone used to define features of the blades, from a forward perspective.

FIGS. 3, 4 and 5 illustrate variations in blade outlines.

FIG. 6 provides an additional illustration of the form of the propeller blades in relation to a hypothetical cone used to define features of the blades, from a forward perspective.

FIG. 7 illustrates the form of the propeller blades in relation to a hypothetical cone used to define features of the blades, in an aft view of the propeller.

DETAILED DESCRIPTION OF THE INVENTIONS

FIG. 1 is an aft perspective view of a marine propeller with blades having surfaces conforming to the surface of a cone. The propeller 1 includes blades 2 disposed about and mounted on a hub or boss 3. Each blade is characterized by a leading edge 4, a trailing edge 5, a tip 6, a root 7, a thrust surface 8 (also referred to as the blade face, the pressure surface or the aft surface), and a blade back (the forward surface or suction surface) 9. The hub is typically terminated in a cap 10, and is characterized by a hub axis 11. The hub axis is the axis of rotation of the propeller. As shown in the illustration, the leading edge of each blade is forward of the trailing edge. Each blade is characterized by a blade center axis 12 (also referred to as the radial axis), which may or may not be perpendicular to the hub axis 11 (the blade center axis may or may not be located in the geometric center of the blade). (The radial axis in this illustration corresponds to the generator line of a cone used as a reference to define aspects of the blade, as shown in FIGS. 2, 6 and 7). A leading-to-trailing line 13, perpendicular to the radial axis 12, is referred to herein as a pitch line. The hub axis 11 and the blade center axis 12 of blade lie in plane 14.

FIG. 2 illustrates the form of the propeller blades in relation to a reference cone used to define features of the blades, from a forward perspective. The reference cone 21 is characterized by a vertex (apex) 22, a round (preferably circular) base 23, a vertical axis 24 and any number of generator lines exemplified by generator line 25. The cone may be a right cone (the vertical axis 24 passes through the center of the circular base at a right angle), or an oblique cone with a circular or elliptical base, though a right circular cone is preferred because it can provide parabolic curvature on the blade surfaces. In reference to the reference cone, the thrust surface of the blade conforms to a section of the reference cone, such as section 26, centered on the generator line 25, which establishes the radial axis 12 of the blade shown in FIG. 1. The hub 3 is shown in relation to the reference cone, intersecting the surface of the cone and centered on the same generator line as the section of the reference cone. The hub and hub axis are preferably displaced from the vertex of the reference cone, toward the section 26, but may be coincident with the vertex. The hub axis 11 may be oriented perpendicular to the surface of the reference cone so that it intersects the generator line at a right angle and also intersects the cone axis (at an angle dependent on the vertex angle) or angled relative to the surface of the cone (left or right about the generator line) while intersecting the generator line at a right angle (this provides the twist necessary for a symmetric blade), and may also be angled relative to the radial axis/generator line while also intersecting the cone axis 24 (this provides rake) and may also be angled relative to the radial axis/generator line while also not intersecting the cone axis 24 (this provides twist and rake). Thus, the hub axis 11 may intersect the generator line at a right angle, or at an acute or obtuse angle relative to the thrust surface of the blade or corresponding section of the reference cone. (Correspondingly, the resulting blade may be raked forward or aft on the hub.) Also, the hub axis may intersect the cone axis 26 (lie in the same plane) or depart from the cone axis. (Correspondingly, the resulting blade will be twisted or rotated about the blade center axis relative to the hub axis, to set the leading edge forward of the trailing edge). Each blade may be rotated about its generator line, or trimmed asymmetrically about its blade center axis, such that its average pitch angle relative to the hub is different from that which it would have had without such rotation or trimming.

FIGS. 3, 4 and 5 illustrate possible blade outer contours. The blade outline may be, elliptical (27) as shown in FIG. 3, circular (28) as shown in FIG. 4, wedge shaped 29, as a wedge bounded by two generator lines spaced from the generator line 25 with the straight-cut tip as shown, in FIG. 5. The blade outline may be slightly or highly skewed, arc-tipped, scimitar-shaped, or any other shape that provides thrust.

FIG. 6 provides an additional illustration of the form of the propeller blades in relation to a hypothetical cone used to define features of the blades, from a forward perspective. In this view, several of the blades 2, 2′ and 2″ are shown, with one blade 2 superimposed on the surface of the reference cone 21, which in this illustration is a 90° right cone, with a 45° angle between the vertical axis 24 and the generator line 25. This Figure shows the hub axis 11 which is perpendicular to the generator line 25, but does not intersect the vertical axis 24. This makes clear that, for blades conforming to the surface of a right cone, planes perpendicular to the hub axis 11 will intersect the thrust surfaces along parabolic curves, and planes parallel to the hub axis 11 will also intersect the thrust surfaces along parabolic curves. The blades 2′ and 2″ are shown projecting out of the surface of the reference cone, along with corresponding generator lines 25′ and 25″.

FIG. 7 illustrates the form of the propeller blades in relation to a hypothetical cone used to define features of the blades, in an aft view of the propeller. In this view, the blade 2 is shown with its radial axis 12 perpendicular to, and/or coplanar with the hub axis, and as mentioned in relation to FIG. 2, disposed on the same generator line that defines the blade thrust surface 8. This is an aft view, looking at the thrust surface of the blades.

The blade surface curvature of the thrust surface along a rake line is zero, while the blade surface curvature along a pitch line 13 (perpendicular to the rake line/generator line, which may be a line representing the intersection of a plane perpendicular to the cone generator line with the blade surface) is circular. The rake line, which is a line created by the intersection of a plane on which the hub axis lies with the thrust surface is also a generator line of the reference cone. The pitch line is a circular line, projected onto the thrust face at any radius from the center of the hub.

As described above, the propeller comprises a hub operable to rotate about an axis of rotation in a direction of rotation, characterized by a forward end and an aft end, and one or more of the blades each characterized by a root, a tip, a leading edge and a corresponding trailing edge, and a thrust surface. The thrust surface of each blade conforms to a surface of a reference cone characterized by a vertex and a base, and a generator line, wherein a radial axis extending radially from the root of the blade to or toward the tip area of the blade corresponds to a generator line of the reference cone, and the root of the blade is fixed to the hub such that the axis of rotation lies in the same plane as the radial axis of the blade. The axis of rotation and the radial axis of the blade may be substantially perpendicular or set at an angle of 45° or more. Correspondingly, the plane of rotation perpendicular to the axis of rotation may be substantially parallel or set at an angle of 45° or less either forward or aft (a rake angle). The leading edge of each blade is forward of its corresponding trailing edge. The average pitch angle between the leading and trailing edges may be 45° or less. The pitch angle may increase from leading to trailing edge, and decrease from root to tip.

As a result of the relationship between the hub and blade, a line on the thrust surface, along the axis of the blade, is a straight line corresponding to a generator line of the cone, and the shape of the blade thrust surface, along a leading-to-trailing line perpendicular to the radial axis, is a circular arc. Where the hub is displaced from the vertex of the reference cone, as shown in FIGS. 2, 6 and 7, there may be only a single straight line corresponding to a generator line of the cone on the thrust surface. The shape of the blade thrust surface, along a leading-to-trailing line perpendicular to the reference cone vertical axis, where the reference cone is a right cone, is a circular arc. Sections of the blades cut by planes parallel to the plane of rotation, and perpendicular to the axis of rotation (the hub axis), are parabolic. If the reference cone apex is less than 90°, cross-sections parallel to the axis of rotation and not intersecting the axis of rotation are elliptical; if the reference cone apex is 90°, they are parabolic; and if the reference cone apex is greater than 90° they are hyperbolic.

In terms of the reference cone, the blade is disposed with respect to the hub axis so that a plane containing the propeller axis (that is, the propeller axis lies in that plane) will also contain a generator line (that is, the generator line lies in that plane) of the cone which corresponds to a long axis of the blade, such that the blade may have circular or conical curvature in transverse directions, across the thrust surface, between the leading and trailing edges of the blade and substantially no curvature in a direction radial of the blade. The blades may be non-raked, such that the generator line of the cone is perpendicular to the hub axis, or raked such that it is angled relative to the hub axis such that the tip of the blade is forward or aft of the root of the blade. The blade back of each back may have various curvatures, for example to create an airfoil cross section of the blade to increase suction. Each blade may be sharpened, chamfered or faired on its edges, or thickened, strengthened, or faired at or near its hub or boss.

Though the inventions have been illustrated with four-bladed marine propellers, the propeller may be made with any plurality of blades (or even a single blade), and may be adapted for aeronautical use. The description above has been provided in reference to right-hand propellers (rotating clockwise when viewed from aft), but the same principals apply to left-hand propellers.

While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions. The elements of the various embodiments may be incorporated into each of the other species to obtain the benefits of those elements in combination with such other species, and the various beneficial features may be employed in embodiments alone or in combination with each other. Other embodiments and configurations may be devised without departing from the spirit of the inventions and the scope of the appended claims. 

1. A propeller comprising: a hub operable to rotate about an axis of rotation in a direction of rotation, characterized by a forward end and an aft end; and one or more blades characterized by a root, a tip, a leading edge and a corresponding trailing edge, and a thrust surface, wherein the thrust surface of each blade conforms to a surface of a reference cone characterized by a vertex and a base and a reference cone circumference, and a generator line, wherein a radial axis extending radially from the root of each blade corresponds to a generator line of the cone, and the root of each blade is fixed to the hub such that the axis of rotation is coplanar with the radial axis of each blade; wherein each blade subtends no more than 90° of the reference cone circumference.
 2. The propeller of claim 1 wherein: the axis of rotation and the radial axis of each blade are substantially perpendicular.
 3. The propeller of claim 1 wherein: the axis of rotation and the radial axis of each blade are set at an angle of 45° or more.
 4. The propeller of claim 1 wherein: the leading edge of each blade is forward of its corresponding trailing edge.
 5. The propeller of claim 1 wherein: each blade is rotated about its generator line such that its average pitch angle relative to the hub is different from that which it would have had without such rotation.
 6. The propeller of claim 1 wherein the average pitch angle between leading and trailing edges is 45° or less.
 7. The propeller of claim 1 wherein: a line on the thrust surface, along the radial axis of each blade, is a straight line corresponding to a generator line of the cone.
 8. The propeller of claim 1 wherein: a leading-to-trailing line on the thrust surface of each blade, perpendicular to the radial axis, is a circular arc.
 9. The propeller of claim 1 wherein: each blade is symmetric about the radial axis of the blade.
 10. The propeller of claim 1 wherein: each blade is asymmetric about the radial axis of the blade.
 11. The propeller of claim 1 wherein: the plane containing the radial axis and axis of rotation is substantially parallel to a plane containing a portion of the trailing edge of the blade.
 12. The propeller of claim 1 wherein: the hub is spaced apart from the vertex of the reference cone, such that the axis of rotation intersects a generator line at a distance of at least half the length of the distance from the blade root to the tip as measured along the generator line that passes through the axis of rotation.
 13. The propeller of claim 1 wherein: a plane which passes through a portion of the blade near its trailing edge is substantially parallel to a plane containing the radial axis of the blade and its axis of rotation.
 14. A propeller characterized by a propeller axis, said propeller comprising: a blade having a thrust face which substantially conforms to an area of the curved surface of a cone, said blade having a radial axis; said blade being disposed with respect to the propeller axis so that a plane containing the propeller axis will also contain a generator line of a reference cone which corresponds to a radial axis of the blade.
 15. The propeller of claim 14 wherein: the blade has a circular curvature in directions transversely between the leading and trailing edges of the blade and no curvature in a direction radially of the blade.
 16. The propeller of claim 14 wherein: the blade has the curvature of a conic section in directions transversely between the leading and trailing edges of the blade and no curvature along a radius of the blade.
 17. The propeller of claim 14 wherein: the blade, in addition to being disposed with respect to the propeller axis so that a plane containing the propeller axis will also contain a generator line of the cone which corresponds to a long axis of the blade, is disposed such that the generator line of the cone is perpendicular to the propeller axis.
 18. The propeller of claim 14 wherein: the blade, in addition to being disposed with respect to the propeller axis so that a plane containing the propeller axis will also contain generator line of the cone which corresponds to a long axis of the blade, is disposed such that the generator line of the cone is angled relative to the propeller axis such that the tip of the blade is forward or aft of the root of the blade.
 19. A propeller comprising: a hub operable to rotate about an axis of rotation in a direction of rotation, characterized by a forward end and an aft end; and one or more blades characterized by a root, a tip, a leading edge and a corresponding trailing edge, and a thrust surface, wherein the thrust surface of each blade conforms to a surface of a reference cone characterized by a vertex and a base and a reference cone circumference, and a generator line, wherein a radial axis extending radially from the root of each blade corresponds to a generator line of the cone, and the root of each blade is fixed to the hub such that the axis of rotation is coplanar with the radial axis of each blade; wherein the blade's axis of rotation intersects a generator line at a distance of at least half the length of the distance from the blade root to tip as measured along the generator line that passes through the axis of rotation and up to approximately the length of the blade's radial axis away from the cone's vertex. 